The invention generally relates to oscillating piston engines. More specifically, the invention relates to an oscillating piston engine of the type comprising a housing in which at least one piston is arranged which can revolve in the housing about an axis of rotation which is fixed in relation to the housing, and which performs when revolving about the axis of rotation reciprocating pivoting movements about a pivot axis extending perpendicularly to the axis of rotation between a first end position and a second end position, the at least one piston having a first running element which runs, as the piston revolves about the axis of rotation, along at least one control cam which is configured in such a way that the pivoting movements of the at least one piston are derived from the revolving movement of the running element along the control cam.
Oscillating piston engines and in particular an oscillating piston engine according to the present invention can be used as internal combustion engines, as pumps or as compressors. An oscillating piston engine according to the present invention is preferably used as an internal combustion engine and is described as such in the present description.
In the case of the use of an oscillating piston engine as an internal combustion engine, the individual working strokes of admitting, compressing, expanding and expelling are imparted by reciprocating pivoting movements of the at least one piston between two end positions.
In the case of the oscillating piston engine known from document WO 03/0670333 A1 from the same Applicant, a total of four pistons are arranged in the spherical housing which jointly revolve about an axis of rotation which is central to the housing and fixed in relation to the housing and perform when revolving in the housing reciprocating pivoting movements about a pivot axis, each two adjacent pistons pivoting in opposite directions. In the case of this known oscillating piston engine, each two pistons diametrically opposing the center of the housing are rigidly connected to each other to form a double piston, and two such pairs of pistons are arranged crosswise in the center of the housing. A respective working chamber is formed between each two mutually facing end surfaces of the pistons of the pairs of pistons, so that the known oscillating piston engine has a total of two working chambers. Both working chambers, which are arranged diametrically opposing the center of the housing, increase and decrease in size in the same direction during the reciprocating pivoting movement of the pistons.
The pivoting movements of the at least one piston are delimited by a first end position and a second end position. The first end position, in which the working chamber has a minimum volume, is referred to as the TDC (top dead center) position and the second end position, in which the working chamber has a maximum volume, as the BDC (bottom dead center) position.
In order to derive the pivoting movements of the at least one piston from its revolving movement about the axis of rotation, the at least one piston has a running element which runs along a control cam formed in the inner wall of the housing itself or on a cam piece connected to the housing inner wall. The control cam extends around the axis of rotation and is configured to be curved in accordance with the reciprocating pivoting movements to be brought about, i.e. has regions which are set further apart from the axis of rotation and regions which are set less far apart from the axis of rotation.
Especially in the case of a configuration of an oscillating piston engine of this type in which in the TDC position the at least one piston is located in proximity to the axis of rotation, while in the BDC position it is set further apart from the axis of rotation, the centrifugal force resulting from the revolving movement of the at least one piston about the axis of rotation assists the movement of the piston from the TDC position to the BDC position. At low rotational speeds, in particular during start-up of the oscillating piston engine, these centrifugal forces are however low. A second oscillating piston is present in the housing on the opposing side of the pivot axis, which second piston is in the process of performing the expanding working stroke after ignition of a fuel/air mixture, while the at least one first piston is in the process of performing the drawing-in working stroke, it can occur that the pressure bank which builds up as a result of the expanding working stroke brakes the pivoting movement of the first piston from the TDC position to the BDC position, thus preventing the first piston from reaching the BDC position in due time with direct and secure contact of its running element on the control cam.
However, also at high rotational speeds, at which there is a sufficient centrifugal force to assist the pivoting movement of the at least one piston from the TDC position to the BDC position, the centrifugal forces in the TDC position are still small, and the risk cannot be ruled out that the running element of the at least one piston does not run along the control cam with the required precision, but rather loses its contact with the control cam, as a result of which the pivoting movement of the at least one piston can be inconstant. This means that the pivoting movement of the at least one piston can at certain points be interrupted or at least slowed down, while in other regions it is then sped up. This can even give rise to the undesired scenario that the at least one piston reaches its BDC position late or not at all. This impairs the running properties, in particular the smoothness of running of an oscillating piston engine of this type.